Chemical Mechanism
Polymer breakdown occurs when water molecules cleave covalent bonds within a molecular chain, resulting in reduced material integrity over time. Hydrolytic degradation typically attacks ester, amide, or ether linkages in thermoplastic resins and thermosetting encapsulants used in printed circuit board construction. This reaction happens whenever humidity levels exceed specific thresholds within the polymer matrix.
High ambient temperatures accelerate the diffusion of water vapor, which increases the frequency of bond scission events.
Environmental Consequence
Moisture absorption inside a completed assembly triggers structural loss in dielectric adhesives and protective coatings. Hydrolytic degradation diminishes the mechanical strength of epoxy resins by turning long chains into shorter fragments with lower glass transition temperatures. When these polymers soften, they lose their ability to support internal conductors during thermal cycling.
Component attachments and solder joints suffer additional stress as the compromised resin fails to distribute mechanical loads properly. Cracked interfaces permit further ionic contamination to reach sensitive circuit paths.
Measurement Protocol
Accelerated aging tests quantify vulnerability by exposing samples to elevated temperature and humidity conditions for prolonged periods. Practitioners evaluate hydrolytic degradation by measuring the change in tensile modulus or mass loss of a resin coupon after removal from a controlled pressure vessel. Quantitative results define the shelf life of raw materials and the reliability of finished boards in tropical or high humidity environments.
Resistance to this phenomenon governs the selection of base laminates and conformal coatings in aerospace applications.
